C9- Transport in Plants Flashcards
Why do plants need a transport system
4
High metabolic demands in areas of plant without glucose- glucose must be transported from source to sink to be used for aerobic respiration
Hormones and mineral ions needed across plant
size- transport systems needed to bridge distances between roots and leaves
SA:V- cannot rely on simple diffusion alone to meet metabolic demands of the plant
What is a vascular bundle
The transport system in plants, made up of the phloem and the xylem
Monocot vs Dicot
Leaf ventillation
Monocot- parallel
Dicot- feathered and palmate leaf
Monocot vs Dicot
vascular bundles
Monocot- vascular bundles are random
Dicot- Vascular bundles in a ring
phloem on outer ring, xylem on inner ring
Monocot vs Dicot
Flowers
Monocots- Sepals, petals, anthers always come in multiples of 3
Dicots- Sepals, petals and anthers never come in multiples of 3
Monocot vs Dicot
Roots
Monocot- fibrous roots with many branches
Dicot- Tap root with fibrous roots attached
Tree girdling
Remove outer layer of bark, severing the phloem, preventing translocation
kills tree efficiently
Scars forms and tree bulges just above due top build-up of sap and movement of water by osmosis
Shape of xylem and phloem in dicots roots
X xylem
0 in each quadrant of X are phloem
Xylem function
Transports water and dissolved minerals upwards from the soil (roots) to the aerial parts (stems and leaves) of the plant by the process of transpiration
Xylem also provides structural support.
Phloem function
Transports soluble organic substances (sucrose) throughout the plant by translocation – from where they are produced (source) to where they are used (sink)
Xylem structure
5
Spirals of lignin so tube does not collapse under transpiration pull and waterproof
Non lignified pits allow lateral movement of water between vessels and cells
parenchyma- stores food, also has tannin which is bitter to deter attack by insects
Narrow- increases adhesion, aiding upwards movement of water by capillary action
one way flow
Phloem structure
4
two way flow
sieve tube elements joined end to end
living cells- cytoplasm of tube element connected to companion cell
Companion cell has many mitochondria to produce ATP for active transport
Three types of cells found in phloem tissue
sieve tube element
companion cell
parenchyma
How does structure of xylem differ form cell walls in typical plant cells
Thicker
Lignified
Contains pits
Moss have no vascular tissue
Why may this effect the size it can grow
No support from vascular tissues
remains small
maintains short diffusion pathway and large SA:V
transpiration vs transpiration stream
Transpiration is the evaporation of water form the leaves and the transpiration stream is the movement of water form the roots to the the rest of the plant through the xylem
Transpiration stream mechanism
6
water evaporates from mesophyll cells, lowering their water potential
water moves out of xylem into the cells by osmosis
Water molecules form H bond with the carbohydrates in the walls of the xylem- adhesion
form H bonds between molecules- cohesion
This pull water up in a continuous column- the transpiration pull
results in tension in xylem aiding the movement of water into the roots
Evidence for cohesion tension theory in plants and trees
when xylem vessels are broken air is drawn in and not water leaking out
When a xylem is broken, a plant cannot move water up the vessel as the continuous stream is broken
in day, diameter of tree trunk shrinks, tension in xylem pulls it in
Factors affecting transpiration
light intensity
increasing light intensity increases the number of open stomata
increasing the rate of loss of water vapour
Factors affecting transpiration
relative humidity
Total amount of water in the air compare to the total amount of water that the air can hold
affect concentration gradient for water
Factors affecting transpiration
Temperature- 2 ways
increases kinetic energy of water molecules so they evaporate more readliy
increased temperatures mean air can hold more water, shallowing the concentration gradient
Factors affecting transpiration
Air movement
affects concentration gradient for water vapour to diffuse out of the leaf
Factors affecting transpiration
soil water availability
if very low the plant will be under stress and transpiration rates will be very low
Using the term water potential can you explain how water might continue to move into the root hair cell
Cells have a higher concentration of minerals and sugars so will have a LOWER WATER POTENTIAL
Soil has very low levels of dissolved minerals so will have a HIGH WATER POTENTIAL
Water will therefore move INTO the cells from a high water potential to a low water potential
Plasmodesmata
define
Microscopic canals that passes through adjacent plant cell walls
allows direct communication of molecules between adjacent cells
Symplast pathway
Symplast = cytoplasm
All cells are connected through plasmodesmata
Water moves through the connecting cytoplasm
Water will move from a high water potential to a lower water potential
Why is the apoplast pathway ‘faster’ than the symplast pathway?
In the apoplast pathway, water forms hydrogen bonds with surrounding molecules, and walls
cohesion and adhesion
Apoplast pathway
Apoplast = cell wall
Water also moves through the connecting cell walls
Cohesion and adhesion allows a continuous flow of water through these fibres
The pull from the xylem causes a continuous flow
The casparian
strip
The casparian strip is waxy and BLOCKS the flow of water through the cell walls
Water is therefore forced back into the symplast pathway from the apoplast pathway
How are root hair cells adapted to their function
4
Microscopic size means they can penetrate between soil particles
Many root hair cells with large SA:V
Each cell has a short diffusion pathway
Many mitochondria to provide ATP for active transport
Movement of water into the xylem
water moves across root through both apoplast and symplast pathways until it reaches endodermis (layer of cells surrounding vascular tissue)
meets the casparian strip
apoplast pathway forced into the cell joining the symplast pathway
must pass through selectively permeable membrane- moves potentially toxic residues
Evidence for the role of active transport in root pressure
root pressure disappears when plant given cyanide, Cyanide stops ATP production so no active transport so no root pressure
if levels of respiratory substrates fall, so does root pressure
root pressure increases with rise in temperature, so a chemical reaction must be involved
Root pressure
active pumping of mineral ions in to the xylem from the endodermis cells to alter water potential and move water by osmosis
independent of transpiration
gives water a push up the xylem
how does water move from the xylem to the root hair cells
the symplastic and apoplastic pathways
How does water move from xylem to cells and then transpiration
water moves into spongy mesophyll and then evaporates into surrounding air spaces
leaves via apoplastic pathways
as water evaporates water potential maintains the transpiration stream
what type of process is the controlling of the size of the stomata opening
turgour driven process
Describe the process of the controlling the size of guard cell openings
Low turgor the asymmetric configuration of the guard cell walls causes it to close
When environmental conditions are favourable the guard cell pumps in solutes by active transport increasing turgor
Cellulose hoops prevent expansion, inner wall less flexible then outer wall cause the stomata to become bean shaped
What is the source and sink in a plant
Source- origin of glucose
Sink- Destination of glucose
What is an assimilate in plant transport
general term for what is being transported through the phloem
Why is sucrose transported in pant and not glucose
Less metabolically active
also soluble
less likely to be used up for respiration while being transported
Translocation
Apoplast pathway from source to phloem vessel
Sucrose is moved into the cytoplasm across the cell membrane – this process is ACTIVE
moves by co transport across cell membrane form the cell wall to cytoplasm to join the simplastic pathway
Translocation
Symplast pathway from source to phloem vessel
Sucrose is moves through the cytoplasm and plasmodesmata
Passive process- diffusion only
Cotransport of sucrose from apoplast to symplast pathway mechanism
protons leave membrane by a proton pump
then re-enter the membrane down the sucrose concentration gradient with a molecule of sucrose in a co transporter
Why does water move from xylem to phloem in translocation
As there is a large amount of sucrose in the phloem it will have a LOW water potential.
Water will therefore move from the xylem (which has a higher water potential)
Does water move by osmosis or diffusion from the xylem to the phloem
water diffuses as it leaves non lignified pits and then the plasmodesmata so never crosses a membrane
Where does movement in the phloem originate from
As water moves in it will increase the hydrostatic pressure – and force movement in the phloem
IN BOTH DIRECTIONS
Translocation
Unloading
The sucrose unloads where it is required and will simply diffuse down a concentration gradient.
The sucrose is quickly converted to glucose (used in respiration) or starch (storage) so that the concentration gradient is maintained
Evidence for the mass flow hypothesis
Advances in microscopy allow us to look at the companion cells- many mitochondria so must be active
If use cyanide to poison the companion cell translocation stops
flow is around 10 000 times faster than diffusion so there must eb an active process involved
Ion that is involved in the cotransport of the loading of the phloem
H+
(proton)
Xerophytes
general classification
Plants that live in dry habitats and have adaptations to conserve their water
enables them to live and reproduce in areas with low water availability
Hydrophytes
general classification
plants that live in water
have and need adaptations to cope with growing in water or permanently saturated soil
if water logged the air spaces fill with water and not air
4 key xerophyte adaptations and what they do
Thick waxy cuticle- reduce water loss by transpiration
sunken stomata and hairy leaves- maintain a humid and still microclimate reducing concentration gradient
leaf loss- loose leaves when water not available, trunk turns green to photosynthesise
root adaptations- long deep tap rots or wide shallow roots to increase access to water
5 Hydrophyte adaptations and what they do
Stomata on upper side of leaves and always open- maximum gas exchange, water loss is ok as much more available, on upper side so exposed to air
wide flat leaves- capture as much light as possible for photosynthesis
no waxy cuticle- no need to conserve water as plenty is available
air sacs- To allow plant to float to the surface of the water
small roots- water can diffuse directly into stem and leaf tissue
Potometer method
airtight potometer
dry leaves and cut stalk at a slant underwater
measure time taken for air bubble to travel a known distance
calculate volume of water uptake
maintain constant conditions
